Ronald Dworkin, a legal philosopher and public intellectual of bracingly liberal views who insisted that morality is the touchstone of constitutional interpretation, died Thursday in London. He was 81. . . .

Professor Dworkin was “the primary legal philosopher of his generation,” said Judge Guido Calabresi, a former dean of Yale Law School who now sits on the federal appeals court in New York. He was also one of the most closely read as a mainstay of The New York Review of Books, to which he contributed articles for decades.

Professor Dworkin’s central argument started with the premise that the crucial phrases in the Constitution — “the freedom of speech,” “due process of law,” “equal protection of the laws” — were, as he put it, “drafted in exceedingly abstract moral language.”

“These clauses,” he continued, “must be understood in the way their language most naturally suggests: they refer to abstract moral principles and incorporate these by reference, as limits on the government’s power.”

It is not hard to hear echoes of Professor Dworkin’s approach in the writings of Justice Anthony M. Kennedy, who often holds the crucial vote in morally charged debates before the United States Supreme Court and is quite likely to play a decisive role in two pending cases on same-sex marriage.

“The dominant voice you hear,” Professor Dworkin said, “is about justice and injustice and what a decent society will tolerate and what it won’t.”

Thomas Nagel, a philosopher and Professor Dworkin’s partner in a colloquium in legal, political and social philosophy offered for many years at New York University, said in a 2007 tribute that his friend’s analytic power was amplified by the vigor and verve of his writing. Professor Dworkin, he said, could “explain difficult moral issues about law, politics and society in lucid terms to a general nonacademic audience — without in any way watering them down or simplifying them.”

His critics said Professor Dworkin’s approach was a smokescreen. “Dworkin writes with great complexity but, in the end, always discovers that the moral philosophy appropriate to the Constitution produces the results that a liberal moral relativist prefers,” Robert H. Bork, the former Supreme Court nominee who died in December, wrote in 1997 in “The Tempting of America.”

Judge Richard A. Posner, who sits on the federal appeals court in Chicago, wrote in a 2001 study of public intellectuals that Professor Dworkin’s popular writings were slippery, partisan and predictable. “Dworkin’s dominant bent as a public intellectual,” Judge Posner wrote, “is to polemicize in favor of a standard menu of left-liberal policies.” . . .

After graduating from Harvard Law School, Mr. Dworkin served as a law clerk to Judge Learned Hand, a federal appeals court judge in New York and a towering figure in the law. In a letter to Justice Felix Frankfurter of the United States Supreme Court, Judge Hand called the young man “the law clerk to beat all law clerks,” a compliment he undermined only slightly by calling him “Roland Dworkin.”

Mr. Dworkin turned down an opportunity to serve as a clerk to Justice Frankfurter, a decision he later called “a very serious mistake.” . . .

Professor Dworkin’s most influential book was “Law’s Empire,” on the nature and role of adjudication. It was among the most-cited books on law of the last century. He also wrote “Life’s Dominion,” on abortion, euthanasia and the questions they raise; “Sovereign Virtue,” on equality; and three collections of essays, “Taking Rights Seriously,” “A Matter of Principle” and “Freedom’s Law.”

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